This invention relates to a mine support or pre-stressing bag of the type which is adapted to be placed between the hanging wall and the top of a support pack or timber pack and then filled with a settable grout under pressure to place a pre-stress on the pack.
The aforementioned type of support bag is known and is used reasonably extensively in the mining industry. The advantage of using a support bag is that the hanging wall is supported immediately by the pack so that no settling of the hanging wall is necessary in order for the pack to take up its load. This reduces fracturing of the hanging wall and hence maintains the integrity of the hanging wall thereby reducing the chances of rock falls and like hanging wall failures.
Prior art support bags have generally comprised two types of bag, namely weeping bags which are designed to allow liquid pumped into the bag to weep as the grout within the bag sets and, non-weeping bags which are basically liquid impervious. This invention is concerned with non-weeping type bags. Non-weeping bags have in the past suffered from various disadvantages. These generally concern leakage which can arise from various causes, such as abrasion of the bag, or failure at a join in the bag. Leakage frequently occurs at points where the fabric sheet from which the bags are made is joined, particularly where the joins are stitched together. In extreme cases leakage can result in the failure of the bag which can, in turn, lead to a catastrophic failure of the support.
One prior art bag which has proved reasonably successful in practice comprises an inner impervious bag and one or more outer high strength bags. The impervious bag is protected against external abrasion by the outer bags and the outer bags tend to protect the inner bag against rupture by constraining the inner bag. This allows the inner bag to withstand high internal pressures.
This type of mine support bag is, however, reasonably expensive to produce. Also, failures can occur, particularly where the inner bag is crimped or folded for some reason or where the inner bag is imperfectly restrained. Assembly of such composite bags has also been found to be both time consuming and labour intensive.